1. Field of the Invention
This invention relates to a control device in an image processing apparatus for controlling the execution timing of the sequence of a plurality of process means which execute image formation.
2. Description of the Related Art
Along with the development of microcomputers, the imaging forming loads heretofore controlled by a relay sequence circuit or a logic circuit comprising a combination of ICs have come to be realized by the program control of the microcomputer.
The respective image forming loads which should originally be parallel-controlled have become time-divisionally controlled by program control as microcomputerization has advanced, and parallel control has been realized.
However, time-divisional control by program is not suited for control in which high-speed responsiveness is required. Therefore, the control of such parts has been accomplished with by making a microcomputer correspond to a load or by adding a hardware circuit for exclusive use.
These will be described by taking a copying apparatus as an example.
FIG. 2 of the accompanying drawings shows the construction of a copying apparatus to which the present invention is applicable. An original is slit-illuminated by original illuminating means 100 such as a fluorescent lamp, and the image of the original is formed on a photosensitive drum 108 by a zoom lens 107. The light reflected then from the original is directed to the photosensitive drum 108 via a first mirror 101, a second mirror 102, a third mirror 103, the zoom lens 107, a fourth mirror 104, a fifth mirror 105 and a sixth mirror 106.
The original illuminating means 100 and the first mirror 101 are moved in the direction of the arrow in synchronism with the rotation of the photosensitive drum 108 in the direction of the arrow. At one half of the speed of the original illuminating means and the first mirror, the second mirror 102 and the third mirror 103 are moved in the direction of the arrow. This results in the length of the optic axis 109 being constant.
After the first mirror 101 has been moved by an amount corresponding to the length of the original, the first mirror is reversed and returns to its initial position. The design is such that the position of the leading edge of the original and the basic position of the first mirror can be detected by a leading edge sensor 110 and a scan home position sensor 111, respectively.
Around the photosensitive drum 108, there are provided a primary charger 112, a blank exposure illuminator 113, a developing device 114, a transfer charger 115, a separator 116, a cleaner 117 and a residual charge, eliminator 118. An electrostatic latent image formed by the potential variation caused by the intensity of light of the imaged point of the slit-exposed original is developed and the developed image is transferred to copying paper. The copying paper is discharged by conveying means 119 through a fixing device 120.
Sheets of copying paper are held in an upper cassette 121 or a lower cassette 122, and a sheet of copying paper is picked up by a paper feed roller 123 or a paper feed roller 124 and is temporarily stopped at the position of a resist roller 125.
The first mirror 101 is moved in the direction of the arrow, the time when the leading edge portion of the original is imaged is detected by the leading edge sensor 110, the time during which the imaging position of the photosensitive drum 108 rotates to the position of the transfer charger 115 is measured and time adjustment is effected so that the leading edge of the copying paper at this time is also moved to the position of the transfer charge 115. Whereafter, the resist roller 125 is rotated to thereby effect alignment of the image on the copying paper.
An instrument controlling microcomputer has heretofore been used to control the operation of the above-described copying apparatus.
For example, Model 8049 or 8051 produced by Intel, Inc. corresponds to said microcomputer. For simplicity, the conventional control circuit concerned with the control of the scanning of the optical system and the feeding of copying paper is extracted and shown in FIG. 3 of the accompanying drawings.
In FIG. 3, reference numeral 201 designates the instrument controlling microcomputer. The instrument controlling microcomputer 201 is connected to RAM 202 and ROM 203 through an external bus. Within the microcomputer 201, CPU 210, RAM 211, input port 212, output port 213 and programmable oscillator 214 are connected together through an internal bus 215.
A signal SHP is input to the port A0 of the input port 212 from the scan home position sensor 110 through an input buffer 220, a signal ST is input to the port A1 of the input port 212 from the leading edge sensor 111 through an input buffer 221, and a signal PREG is input to the port A2 of the input port 212 from a paper sensor 126 immediately before being input to the resist roller 215 through an input buffer 222.
The signal SHP is 1 when the original illuminating means 100 is in its basic position, and is 0 when the original illuminating means 100 is not in its basic position, and the signal ST changes from 0 to 1 when the original illuminating means 100 arrives at a position for imaging the leading edge of the original, and is 0 when the original illuminating means 100 is in the other position. The signal PREG is 1 when the copying paper is immediately before the resist roller 125, and is 0 when the copying paper is not.
The original illuminating means 100, the first mirror 101, the second mirror 102 and the third mirror 103 are driven by a DC motor M2. To carry out a stageless magnification change, the reduction or enlargement in the main scan direction is accomplished the zoom lens 107 and the reduction or enlargement in the subsidiary scan direction is carried out with the original scanning speed changed. For this speed adjustment, the DC motor M2 is controlled by the microcomputer 201 through a scan motor controller 230. Port C0 is the output terminal of the programmable oscillator 214 and compares the oscillation frequency thereof with a scan speed target, thereby controlling the DC motor M2. The speed of revolution of the motor is detected from an encoder E, and it is fed back, whereby the scan motor controller 230 controls the speed of the motor M2 so that the motor M2 is kept at a speed conforming to a speed control signal Fs. By setting the signal FW of port B0 to 1, the motor is revolved in such a direction that the original illuminating means 100, etc. are moved forward. By setting the signal RV of port B1 to 1, the motor is revolved in such a direction that the original illuminating means 100, etc. are reversed and by setting the signal BRK of port B2 to 1, a brake is applied.
A signal MM is put out from port B3 which is connected to a main motor M1 through a main motor driver 231. The main motor is used to move driving portions except the scan system, such as the photosensitive drum 108, paper feed rollers 123, 124 and resist roller 125. When the signal MM is set to 1, the main motor M1 rotates at a constant speed, and when the signal MM is set to 0, the main motor M1 is stopped. Signals PIC1 and PIC2 are put out from ports B4 and B5 which are connected to clutches CL1 and CL2, respectively, through hammer drivers 240 and 241. Clutches CL1 and CL2 control the rotation and stoppage of the paper feed rollers 123 and 124, respectively, and when the signals PIC1 and PIC2 are set to 1, the paper feed rollers are rotated, and when the signals PIC1 and PIC2 are set to 0, the paper feed rollers are stopped.
A signal REG is put out from port B6 which is connected to a clutch CL3 through a hammer driver 242. The clutch CL3 controls the rotation and stoppage of the resist roller 125, and by setting the signal REG to 1, the resist roller 125 is rotated, and by setting the signal REG to 0, the resist roller 125 is stopped.
Besides these, there are numerous objects of control of the copying apparatus such as rotating stopping of the developing device, application of a developing bias, application of a voltage to each charger, ON and OFF of the residual charge eliminator, driving of the zoom lens, and display of the operation unit and key input control. The description of these objects of control is omitted herein.
An example of the program by which CPU 210 is operated in such a construction, and by which the copying apparatus is controlled, is shown in FIG. 4 of the accompanying drawings.
At step S301, the initial values of the variables of RAM 202 and internal RAM 211 are substituted into the copying apparatus to thereby effect the initial setting of the copying apparatus.
At step S302, the display of the operation panel and processing of the key input are executed. Analysis of the operator's instruction is executed, and display thereof, and display of the condition of the copying apparatus, are executed.
At step S303, control of the electrophotographic process of the chargers, the developing devices, etc. is executed.
At step S304, control of the supply of copying paper is executed.
At step S305, control of the scanning of the original illuminating means, etc. is executed in synchronism with the supply of copying paper.
At step S306, a stepping motor used to move the zoom lens is driven, whereafter the program returns to step S302 and these processings are repeated.
In so controlling the copying apparatus, execution is effected with a plurality of processings being time-divided.
In such a case, if the original illuminating means passes the position of the leading edge of the original when the operation display processing is being executed, the time of detection of the position of the leading edge of the original is delayed until the turn of the scan system processing comes, whereby the time of starting of the rotation of the resist roller 125 is delayed and thus, the image position on the copying paper may deviate in a forward direction. Therefore, it has been necessary to input the detection of the position of the leading edge of the original to an interruption input terminal and applying an interruption signal to CPU 210. CPU 210 is forcibly informed of the position of the leading edge of the original and the time of starting of the rotation of the resist roller 125 is calculated from that time.
In the foregoing, an example in which a deviation of several ms adversely affects the operation of the instrument has been shown, but generally, control cannot be accomplished by the method in which the program proceeds to the next step after the processing of step S302 to step S306 have been completed. Particularly, steps S303-S305 originally progress concurrently and therefore, concurrent processing become necessary. Accordingly, either operating steps S302-S306 under the basic program such as a real time monitor program or describing steps S303 to S305 in a single program must be selected. In the former system, the time required for the change-over of the processing of each step, namely, the overhead, is great and the utilization efficiency of CPU is reduced. In the latter system, the program becomes complicated and along with the increase in the amount of programming by the improved performance of the control instrument, misprogramming increases and very much time is required for the program.
Even in the case of the former system in which real time monitoring is utilized to effect time-divisional processing, if an attempt is made to effect control of the stepping motor, etc. by a program, noise may be produced unless the program is actuated every predetermined period of time. Therefore, such a program must be executed by constant time interruption processing or the like and, due also to an increase in such interruption processing, the other processes are made to wait for the time during which processing of a high priority is executed in 210. Thus, high-speed parallel processing cannot be realized, and control of the stepping motor and scanning motor is entrusted to another microcomputer. The overhead is increased by the exchange of information between the microcomputers and the change-over of the program being frequently effected under the real time monitor. Thus, the rate at which the CPU effects the processing other than the original control operation becomes high and correspondingly, the amount of hardware becomes large, causing an increased cost.
Further, interruption processing which is used to enhance the responsiveness or the structure of the program is made into a special form, whereby the program becomes debug and more complicated and the time of program debug increased, which leads to an increased general development cost.